With the growing popularity of VoIP, more and more homes and businesses do not have a POTS (plain old telephone service) line.  VoIP is excellent technology for voice calls (hence the letter "V" in "VoIP") but that's about all it's good for. 

Finding a reliable fax solution was interesting to say the least.  Most people we asked for advice told us, "Faxing is archaic technology.  Forget that and use e-mail instead!"  We certainly rarely send faxes, but as long as our customers wish to fax in orders, we are going to need a reliable way of receiving them.  Fortunately, we've found several!

Just the Fax, ma'am.

If you want to use a customary fax machine, you should select both an ATA that supports T.38 and a T.38 provider.  T.38 is a protocol that relays fax data over a network such as the Internet.  Because the data is not converted into an audio signal and compressed, faxing has a much much higher chance of working.  T.38 is also relatively capable of dealing with minor packet loss.

It's true that it is possible to fax over VoIP at very low speed such as 9600 bps without using T.38 but we would not rely on a VoIP fax setup for anything more than a couple of faxes per year. If you really want to try it, Future-Nine has a good set of tips.

Some ATAs that support T.38 are the SPA-2102 and the SPA-3102. (The PAP2T does not support T.38.) Some VoIP providers are also T.38 providers.  We can only recommend two: Callcentric and AcroVoice.  Shaw Cable's Digital Phone service also supports T.38.

When shopping for a T.38 provider, ask if their carrier delivers calls to them over TDM or T.38.  It may be difficult to find this information, but calls delivered to the provider over TDM or T.38 rather than G.711 can increase the reliability of faxing.  The connection between your T.38 provider and their carrier is (hopefully) much less susceptible to packet loss and jitter than a residential-grade internet connection so G.711 between your provider and their carrier is not a dealbreaker.  However, for example, Callcentric's toll-free DIDs are always delivered over TDM.  Their residential DIDs sometimes are.  So in this case, why not take a toll-free DID?

Caveat emptor

Shaw Cable recommends setting fax machines to 9600 bps and turning off ECM/error correction mode.  This is bad advice.  Perhaps this was necessary with the old Motorola modems, but with the new Arris modems, 9600 bps is not necessary.  Our fax works perfectly fine at high speeds.  ECM should not be turned off for the simple reason that if a fax fails, the machine may report a successful send if ECM is turned off.  You will have no idea that the fax actually failed, and the receiver may have no idea that you attempted to send a fax.  So if your fax doesn't work with ECM turned on, it's time to find another fax provider.  Turning off ECM is not a solution!

(Note that Future-Nine's tips that we linked to above suggest turning off ECM.  This probably is necessary to make faxing over VoIP work, and is one of the reasons we do not recommend faxing over VoIP.)

One other fact that is interesting to note is that we cannot fax on line 3 of our 4-line modem.  We have no idea why, and unfortunately not surprisingly, neither does Shaw.

Some users report faxing success without a POTS line only when they place the fax behind an ADSL filter.  We have not found this necessary but include it in case it helps anyone.

Faxing with a PC

For sending faxes without a fax machine, we have had good success with FaxBack's T.38 Plug-in and Callcentric.  We have tried other T.38 software such as T38Modem and Zoiper but try as we might we have not been able to make it work.  We were not able to receive faxes with a Callcentric DID and this plug-in.  (The error was: "An invalid fax number has been detected".  Anyone know how to fix this?)

Callcentric has a feature that will convert incoming faxes to PDF and email them to you.  For us, this worked well in testing, but we were disappointed to discover it incompatible with some of our customers' fax machines.  After we reported the issue nearly a year ago, the feature was marked as "unsupported" and that is still its status at the time of this writing.  Some users report success with it and some don't.

In our situation, we needed to receive faxes without a fax machine, and we wanted to port an existing local number.  It was very difficult to find a company that could port Canadian DIDs and was not SIP-based.  We tested a company called UFAX.NET and we were hopeful because of their salesperson's impressive volume of knowledge.  Unfortunately, as soon as we signed up, the salesperson inexplicably refused to respond to our emails and phone calls.  Their technical support was very slow to respond to queries and was not helpful.  We do not recommend UFAX.NET.

And about time, too.

Fortunately, we found MyFax.  They are not SIP-based. Their packages start at $13 per month which includes 100 pages out and 200 pages in.  It took plenty of encouragement to get their salesperson to answer questions, but eventually he did.  They did successfully port our Vancouver DID.  We have been using them since August 2009 and astonishingly have been problem-free.  MyFax's technical support is absolutely phenomenal.  They happily escalated an issue we were having up three levels of support, and then to their carrier.  (The issue was that MyFax could not receive faxes from Shaw Cable; MyFax could receive faxes from anyone else and Shaw could send faxes to anyone else.) We ended up solving the problem ourselves - it was largely due to an issue with Shaw's equipment.  However we were very grateful for the help that they offered in spite of the fact that the issue was not their fault because it gave us valuable information with which to solve the problem.

So why shouldn't you just send or receive a fax over a regular VoIP line?

Trev from AcroVoice kindly explains why:

"Despite the G.711 codec being lossless, it still suffers from jitter or dropped packets that will cause a fax machine to get confused. These devices rely on precise timing. When a packet is dropped or not received in time, the PSTN gateway will use an algorithm called PLC - packet loss concealment. This is a wonderful thing for us humans as we'll hear an approximation of what the algorithm estimates would have been in that time slot. Without PLC, we would hear drop outs which are much more annoying. With good PLC you probably wouldn't even notice if 2% of packets were being dropped.  Faxes rely on receiving every sound as it is sent. When the sound is estimated based on voice patterns, it will confuse the fax machine. Further, if the jitter buffer attempts to enlarge itself, a PLC algorithm would be required to stretch out the sound over a small period of time so the buffer can grow. Not good for faxing."

Conclusion: Absolutely possible.

Currently, for business faxing, we use Shaw Cable and MyFax for outgoing and MyFax for incoming.  For personal faxing, we use Callcentric with FaxBack's plugin for outgoing.  We are currently helping to beta test a new Canadian VoIP provider based in Victoria that supports T.38.  If it works as well as we anticipate we will be thrilled.  Stay tuned.